1. Field of the Invention
The present invention relates to a technique for reducing cavitation in a system having a low-temperature heat source, and more particularly relates to a system for reducing pump cavitation with which cavitation is reduced very well in a rotary pump used for the supply of a propellant to a rocket engine.
2. Description of the Related Art
At the inlet to a rotary pump, there is a decrease in pressure behind the blades rotating at high speed, and in some cases bubbles can form when the pressure drops below the saturated vapor pressure-locally. This is called cavitation. When cavitation does occur, there is a decrease in the pump intake flux or pump outlet pressure, and at the same time the vibration of the pump may increase to the point that the pump breaks.
Some of the measures that have been taken in the past for avoiding the occurrence of this cavitation include the following.
1. Raising the pump inlet pressure
2. Reducing the pump speed so as to minimize the pressure drop at the pump inlet
3. Decreasing the outside diameter of the pump inlet
In order to increase the payload of a rocket, the overall size and weight of the rocket engine need to be reduced, including reducing the size and weight of the pump system that supplies propellant to the engine. To accomplish this, it is necessary to raise the pump speed so as to increase the attainable pump pressure and also increase the operating pressure of the rocket engine. However, while measures 1 to 3 above do indeed reduce cavitation, they also diminish pump performance so much that the desired high performance cannot be achieved, so the above-mentioned necessity cannot be met. Specifically, with measure 1, the pressure must be raised in the propellant tank, which requires a corresponding increase in the thickness of the tank walls, and this results in greater tank weight. With measures 2 and 3, pump performance is diminished, the operating pressure of the rocket engine cannot be raised, and the specific thrust cannot be increased, among other problems.
The present invention was conceived in light of this situation, and it is an object thereof to reduce the occurrence of cavitation by means of a simple structure, while maintaining pump performance, in a rotary pump (if the pump has an inducer, this refers to the entire pump including the inducer), and to lower the overall weight and size of a rocket engine by improving the propellant supply system of the engine.
The present invention is a pump system in which the temperature of the fluid flowing to the pump is lowered so as to lower the saturated vapor pressure of this fluid, which increases the allowable decrease in fluid pressure and reduces the occurrence of cavitation.
The present invention also involves utilizing a low-temperature source present in the pump system, and using this low-temperature source for heat exchange with the fluid flowing to the pump, thereby lowering the temperature of the incoming fluid and reducing the occurrence of cavitation. In the case of a liquid rocket engine, a coolant or another propellant whose temperature is lower than that of the primary propellant can be employed as this low-temperature source.